I'm gonna go ahead and make a bold statement here, folks.
If you're not invited to go somewhere with somebody or a group of people, it's generally not socially acceptable to go along without asking them if you can go. If you insist on inviting yourself, ask the individual or group first. These are pretty much basic kindergarten manners. If you refuse to abide by them, don't be surprised if we vent about you later on to our friends or give you glances like "What the hay?" when you insert yourself into a conversation in which you have no part or understanding of the context.